Conditional Statements (If-Then-Else)
Definition:
Conditional statements, also known as "if-then-else" statements, are a fundamental concept in computer programming that allows a program to make decisions based on specified conditions. They enable the program to execute different blocks of code depending on whether a condition is true or false. Conditional statements provide a way to control the flow of a program by introducing decision-making capabilities.History:
The concept of conditional statements can be traced back to the early days of computer programming. In the 1950s, programming languages like FORTRAN and ALGOL introduced the idea of conditional execution using "IF" statements. These early implementations allowed programmers to make decisions based on the evaluation of conditions. Over time, the syntax and functionality of conditional statements evolved, and they became a standard feature in most programming languages.- Evaluation of Conditions: Conditional statements revolve around evaluating conditions. A condition is typically an expression that compares values or checks for certain properties. The result of the condition is either true or false.
- Branching: Based on the outcome of the condition evaluation, the program branches into different paths of execution. If the condition is true, one block of code is executed. If the condition is false, another block of code (or no code) is executed.
- Decision Making: Conditional statements allow a program to make decisions. By evaluating conditions and branching accordingly, the program can adapt its behavior based on different scenarios or inputs.
How It Works:
The general syntax of a conditional statement is as follows:```
if (condition) {
// Code block executed if the condition is true
} else {
// Code block executed if the condition is false
}
```
Here's how it works:
- The condition inside the parentheses `(condition)` is evaluated. The condition can be any expression that returns a boolean value (true or false). It can involve comparison operators (`==`, `!=`, `>`, `<`, `>=`, `<=`), logical operators (`&&`, `||`, `!`), or any other valid expression.
- If the condition evaluates to true, the code block immediately following the `if` statement is executed. This block is typically enclosed in curly braces `{}`.
- If the condition evaluates to false, the code block following the `else` keyword is executed (if present). The `else` block is optional and can be omitted if no alternative action is needed.
- After executing the appropriate code block, the program continues with the next statement after the conditional statement.
Conditional statements can be nested, meaning you can have an `if-then-else` statement inside another `if-then-else` statement. This allows for more complex decision-making structures.
Example:
Let's consider a simple example to illustrate the usage of a conditional statement:```python
age = 18
if age >= 18:
print("You are eligible to vote.")
else:
print("You are not eligible to vote.")
```
In this example, the condition `age >= 18` is evaluated. If the value of `age` is greater than or equal to 18, the message "You are eligible to vote." is printed. Otherwise, if `age` is less than 18, the message "You are not eligible to vote." is printed.
Conditional statements are a powerful tool in programming that allows for dynamic behavior based on different conditions. They are widely used for decision-making, input validation, error handling, and controlling the flow of a program. Understanding conditional statements is essential for writing efficient and flexible code that can adapt to various situations.